JPH09189751A - Magnetic sensor - Google Patents

Abstract

(57) Abstract: A magnetic field measuring device for long-time measurement, which can accurately measure a magnetic field even under the influence of radiation, and which is suitable for measuring a magnetic field in a fusion device. A magnetic field strength is obtained by passing a current through a thin plate conductor 1 whose both ends are fixed and measuring a displacement in a plate thickness direction due to an electromagnetic force generated by an interaction with a magnetic field. A magnetic field detector composed of a thin plate conductor 1 fixed at both ends, a power supply for supplying a current to the conductor, a conductor, and a displacement measuring device for measuring the displacement of the thin plate conductor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for detecting a magnetic field, and in particular, when there is a strong magnetic field under radiation and in a direction perpendicular to the measuring magnetic field, the magnetic field strength can be accurately measured even in a nuclear fusion device. It relates to a magnetic field sensor.

[0002]

2. Description of the Related Art In a nuclear fusion device, a dilute hydrogen gas is placed in a donut-shaped vacuum container and an electric current (plasma current) is applied to the gas.
To make hydrogen gas a high temperature plasma. Energy is generated by causing a nuclear fusion reaction in this plasma. The plasma is isolated from the wall of the vacuum vessel by the magnetic field,
Sometimes the plasma becomes unstable and may come into direct contact with the vacuum vessel wall. At this time, the plasma becomes unstable and may disappear. To prevent this, the fusion device holds the plasma stably by measuring the magnetic field around the plasma and controlling the magnetic field strength by negative feedback.

In order to perform such magnetic field control, a dynamic range with good response and a wide range (about 0.0001T) is provided.
A magnetic sensor is required, but a magnetic field change rate is measured by using a pickup coil as such a magnetic sensor, and a signal proportional to the change rate is integrated by an integrator to be proportional to the magnetic field strength. I was getting a signal to do. Hereinafter, this conventional magnetic sensor will be referred to as a coil type magnetic sensor.

FIG. 2 shows a conventional coil type magnetic sensor 11. This sensor is composed of a pickup coil and an integrator 12. Since the coil type sensor 11 has a simple structure, it has been generally used in the conventional fusion experimental apparatus. However, a fatal drawback of the coil type sensor is zero point drift during long-time measurement. That is, this is a phenomenon in which the output signal becomes as shown in FIG. Integrator 1
Since 2 always integrates the signal over time, if there is a non-zero signal cause in the input or in the integrator, the non-zero signal is integrated indefinitely, and finally magnetic field measurement becomes impossible. Therefore, such an integrator has been used for an experiment of measuring time up to about 1 minute at most.

Further, in order to compensate for such a defect, it has been practiced to measure a magnetic field using a Hall element. However, such a semiconductor-type magnetic sensor cannot be used in a radiation environment and cannot be used in a large-scale fusion device.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a magnetic sensor for long time measurement that can be used in a nuclear fusion device. Even in a nuclear fusion device that discharges for a long time, it is possible to measure a magnetic field and grasp the magnetic field distribution and the magnetic field strength. Negative feedback control is possible.

With the conventional coil type magnetic sensor, it is difficult to measure a magnetic field for a long time of about a minute or more due to zero point drift.
In order to solve this difficulty, a magnetic field measurement method that does not use an integrator is necessary. As a concrete method of this, for example, an experiment (MORIYAMA,
S., NAKAMURA, Y., NAGAO, A., JOTAKI, E., NAKAMUR
A, K., HIRAKI, N., ITOH, S., Nucl. Fusion Vol.30
In (1990) P.47.), A magnetic field is measured using a Hall element and plasma discharge for more than one hour is realized by a tokamak device. However, in a magnetic sensor using a semiconductor such as a Hall element, the life of the magnetic sensor becomes insufficient because the semiconductor is severely deteriorated in a radiation environment.

It is an object of the present invention to provide a magnetic sensor that does not use an integrator and semiconductor.

[0009]

[Means for Solving the Problems] From the above discussion, the magnetic sensor used for measuring the magnetic field in the long-time discharge of the fusion device is
It is not desirable to use an integrator. Also, semiconductors such as Hall elements are not desirable. Therefore, in the present invention, the strength of the magnetic field is measured by the electromagnetic force or the deformation caused by the electromagnetic force. When a current I is applied to the conductor, a force F = I × B is generated per conductor unit length due to the interaction with the magnetic field. If this force is measured, the magnetic field can be measured without drift. However, since the deformation is used to measure the electromagnetic force, the amount of deformation is actually measured instead of measuring the electromagnetic force and converted into the magnetic field strength. That is, if the amount of deformation is δ

[0010]

[Equation 1] δ∝F / G (Equation 1) If the rigidity G (second moment of area) of the object to be deformed is isotropic, the deformation is isotropically proportional to F and the directionality of the magnetic sensor also disappears. . On the other hand, the conventional coil-type magnetic sensor has a clear directionality and is characterized in that it can separate magnetic field components. This directional property can be realized by making the rigidity G anisotropic. That is, the rigidity Gm in the measurement direction is reduced, and the rigidity Gp in the direction perpendicular to both the current direction and the measurement direction.
Can be realized by making Gm much larger than Gm. Such Gp >> Gm can be obtained by using a thin plate.

FIG. 4 shows a principle diagram of the magnetic sensor according to the present invention. An electric current is applied to the thin plate conductor 1 in a magnetic field, and the deformation δm in the thickness direction of the thin plate is measured and converted into a magnetic field.

[0012]

## EQU00002 ## B = .delta.mGm / I (Equation 2) A magnetic field is generated due to the influence of an electric current, but the feeder line is arranged so that this magnetic field does not affect the deformation .delta.m. Both ends of the thin plate conductor are fixed to the support 4.

Further, a strong toroidal magnetic field exists in the fusion device, and a poloidal magnetic field in a direction perpendicular to the strong toroidal magnetic field is measured. Therefore, when the present magnetic sensor is arranged in the nuclear fusion device, the direction of the current flowing through the sensor unit is to flow in the direction parallel to the toroidal magnetic field.

When a current is applied to the sensor plate, the thin plate conductor 1 of the sensor part deforms as a beam supported at both ends, and the deformation is proportional to the magnetic field. If this deformation amount 19 is measured and converted into a magnetic field, the magnetic field strength can be measured.

When the sensor portion is formed in a plate shape, for example, when the ratio of the thickness d to the width w in FIG. 4 is set to about 1:32, the rigidity in the measurement direction (plate thickness direction) is about 1000 times that in other directions. Get smaller. In this case, even if there is a magnetic field of 0.5T in the plate width direction, the measurement error magnetic field given to the measurement in the plate thickness direction is 0.000.
It is less than 5T, and the measurement error is 0.1%, which is sufficiently small. As a result, it becomes possible to perform measurement with directionality as in the conventional coil type magnetic sensor, and it is possible to selectively measure the magnetic field in the plate thickness direction.

[0016]

FIG. 1 shows an embodiment of the present invention. The center of the sensor part 9 is the thin plate conductor 1, and the current 3 is flown from the terminal 7 at one end, flows to the other end, and circulates around the peripheral part (sensor frame) to make the terminal 6 at the other end near the original terminal 7. Come back to. The sensor plate fixing portion near the terminal 7 is fixed via the insulating material 2. When a current is applied to the thin plate conductor 1, the thin plate conductor 1 is displaced.

A method for measuring the magnitude of this displacement is shown in FIG. The thin wire resistor 8 is used as the support 4 and the thin plate conductor 1.
Place as shown in the figure. The thin wire resistor 8 arranged on the displacement side of the thin plate has a reduced length, so that the resistance increases, and the thin wire resistor on the opposite side has an extended resistance, which decreases the resistance. This resistance change is measured to measure the amount of displacement of the thin plate sensor unit. That is, the resistance change is proportional to the displacement amount, and the displacement amount is the thin plate conductor 1.
It is proportional to the product IBn of the current I flowing through and the magnetic field strength Bn in the plate thickness direction. Therefore, the resistance change can be converted into IBn by performing sensitivity calibration in advance, and can be converted into the magnetic field strength if I is known. This thin plate type magnetic sensor 9 can obtain a signal proportional to the magnetic field strength without using an integrator, and there is no zero drift which has been a problem in the conventional coil type magnetic sensor 11. In addition, since no semiconductor is used for the sensor unit, the life under radiation is longer than that of a magnetic field sensor using a Hall element. From these points, the magnetic sensor as shown in FIG. 1 is excellent as a magnetic field detector of a nuclear fusion device that operates for a long time. The change in resistivity of the thin wire resistor is measured by, for example, the bridge circuit shown in FIG. 5 below. Arrange the terminals with the numbers indicated by circles as shown in the figure. Voltage output at this time Δ
V is converted into a change in resistance based on the current value.

In the magnetic sensor of the present invention, the thin plate conductor 1 is displaced so that the object moves. For this reason, the frequency response characteristic deteriorates as compared with the conventional coil magnetic sensor. That is, the detection sensitivity of the high frequency component of the magnetic field fluctuation deteriorates. In order to correct this, it is conceivable to use a conventional coil type magnetic sensor to supplement the high frequency component. FIG. 6 shows a measurement system in which a thin plate type magnetic sensor 9 according to the present invention is combined with a displacement detector 10 and a coil type magnetic sensor 11. The output of the coil type magnetic sensor 11 is integrated by the integrator 12 and becomes a signal proportional to the magnetic field. However, the output of the integrator has a time constant of several tens of seconds or more, and drift becomes a problem.
Therefore, the low-frequency drift component is cut by using the high-pass filter 22 having a time constant of about 0.01 Hz or more.
Since the magnetic sensor of the present invention is not accurate in high frequency components, the high frequency components are cut using the low pass filter 21 having the same time constant. Then, as the measurement value, a value obtained by combining the output signals of these two filters through the combining circuit 20 is used. Thereby, the magnetic field can be accurately measured from the high frequency magnetic field fluctuation component to the steady magnetic field.

In the example of FIG. 5, as an example of the method of measuring the displacement of the thin plate conductor 1, a method of measuring the displacement by measuring the change in resistance due to the expansion and contraction of the resistance wire is shown. Here, as an example, FIG. 7 shows an example using an optical fiber. Here, the optical path extends due to the extension of the optical fiber, and when coherent light from the oscillator 13 such as a laser is input from one end of the optical fiber, the phase of the light output from the other end depends on expansion and contraction of the optical fiber. To take advantage of changes. The laser oscillator emits light with a well-defined phase and passes through the demultiplexer 14 toward the sensor. In the thin plate magnetic sensor 9, one optical fiber 18 is fixed to the thin plate conductor 1 and the support 4. The other optical fiber is not fixed and simply passes through. in this case,
The length of the section 23 between the fixing points of the former optical fiber changes according to the displacement amount 19 of the thin plate conductor. On the other hand, the other optical fiber is independent of the displacement amount. The reason why the two optical fibers are arranged alongside each other is to prevent the measurement from being disturbed by the expansion and contraction of the fiber length due to temperature. When the lights from the two optical fibers are made to interfere with each other, the signal output after the interference changes according to the displacement amount 19, and when the signal change is counted by the counter 17, the displacement amount can be estimated and the magnetic field strength can be estimated. However, with this simple method, the sign of the displacement cannot be determined, so the following method is adopted.

Each of these two optical fibers is put into the demultiplexer 14 and demultiplexed into two. Then, it is input to the interferometer as shown in the figure. At this time, a phase shifter is attached to one of the outputs from the demultiplexer of the light that has passed through the optical fiber that senses the amount of displacement. When the phase is shifted by about 90 degrees, the outputs of the two interferometers change in phases different from each other by about 90 degrees when the displacement amount changes, and two interferences occur depending on the changing direction of the displacement amount of the thin plate conductor. The phase relationship of the output of the container (first interference signal 24, second interference signal 25) changes. Although it depends on the shift amount ΔΦ in the phase shifter, FIG. 8 shows how the displacement amount increases or decreases at a constant change rate. When the rate of change is constant, the interference signal is a signal that changes in a trigonometric function with time. However, the relationship between the lead and lag of the phases of both signals is reversed with the increase or decrease of the displacement amount. From this relationship, the direction of displacement can be known. The counter counts changes in these two signals, converts the wave number change into a displacement amount, and outputs a magnetic field signal 26 in which the signal strength is proportional to the magnetic field strength. Thereby, the magnetic field strength can be measured.

[0021]

According to the present invention, a magnetic field can be measured for a long time without using an integrator, and since a semiconductor is not used, it can be used for a long time even in a radiation environment.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional coil type magnetic sensor.

FIG. 3 is a typical magnetic field measurement waveform and magnetic field strength change waveform diagram in the conventional method.

FIG. 4 is a principle diagram of the present invention.

FIG. 5 is an explanatory diagram of a method for measuring displacement of a thin plate conductor according to the present invention.

FIG. 6 is a block diagram of a magnetic field detection system having a high band frequency characteristic using the present invention.

FIG. 7 is a block diagram of the present invention in the case of measuring the displacement of a thin plate conductor with an optical fiber.

FIG. 8 is a characteristic diagram of an output example of the interferometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Thin plate conductor, 2 ... Insulating material, 3 ... Current, 4 ... Support tool,
5 ... Bolt, 6 ... Negative side current terminal, 7 ... Positive side current terminal, 8 ... Thin wire resistor, 9 ... Thin plate type magnetic sensor.

Claims (4)

[Claims] 1. A thin plate conductor whose both ends are fixed and is not easily deformed in the plate width direction is caused to flow an electric current, and a displacement in the plate thickness direction due to an electromagnetic force generated by an interaction between the electric current and a magnetic field is measured. A magnetic sensor characterized by measuring the strength of a magnetic field. 2. A magnetic sensor according to claim 1, which is combined with a magnetic field detector for measuring a high frequency component of the output of the magnetic sensor. 3. The magnetic field sensor according to claim 1, wherein the displacement of the thin plate conductor forming the magnetic sensor is measured by a resistance change due to expansion and contraction of a thin metal wire. 4. The magnetic field sensor according to claim 1, wherein the displacement of the thin plate conductor that constitutes the magnetic sensor is measured by a change in wave number due to expansion and contraction of an optical fiber that transmits coherent light.